Using exercise balls (also known as stability or balance balls) has become a popular way to increase core strength, abdominal fitness, and balance. Exercising with an exercise ball, as opposed to exercising directly on a hard flat surface, forces the user's body to respond to the instability of the ball in order to remain balanced. As a result, the user engages many more muscles, which become stronger over time, thereby improving the user's balance, strength, and fitness. Most frequently, the core body muscles—the abdominal muscles and back muscles—are the focus of exercise ball fitness programs.
Depending on the type of exercise being performed or the fitness or skill level of the user, the level of instability of an exercise ball may need to be adjusted. The level of instability of an exercise ball can be decreased by reducing the pressure within the exercise ball so that the curvature of the exercise ball decreases (i.e., flattens out), making the exercise ball less prone to rolling. Conversely, the level of instability of an exercise ball can be increased by increasing the pressure within the exercise ball so that the curvature of the exercise ball increases, making the exercise ball more likely to roll. Typically, the pressure within an exercise ball can be adjusted by pumping air into or releasing air from the exercise ball through a valve.
Properly adjusting the level of instability of an exercise ball can be difficult. For instance, a pump may be required to increase the pressure within the exercise ball. Using the pump may be complicated and physically challenging for some users. Additionally, it can be difficult to achieve a level of pressure in the exercise ball that corresponds to a desired level of instability. For example, it may be difficult to gauge how much air to pump into or release from the exercise ball in order to achieve the desired level of instability. As a result, a user may pump too much or not enough air into the exercise ball to achieve the desired level of instability. Similarly, a user may release too much or not enough air from the exercise ball to achieve the desired level of instability.
Other exercise devices designed to improve a user's core strength and balance are disclosed in U.S. Pat. No. 6,422,983, U.S. Pat. No. 6,575,885, and U.S. Pat. No. 7,344,488.